ps aux | grep exim
sudo service exim4 status
sudo service exim4 start
netstat -atu | grep smtp
dig @ns1.thegummibear.com thegummibear.com MX
Make sure that /etc/hosts has the fqdn of your mailserver in it. Also, make sure that the same line has a reference to whatever you put in /etc/hostname. Mine looks like this:
/etc/hosts
144.38.199.52 mail.thegummibear.com mail-thegummibear
Because my hostname (in /etc/hostname) was mail-thegummibear
hostname